# RE: Technical problem (OT)

From: Scott <rylos_at_charter.net>
Date: Sat, 25 Sep 2010 09:07:06 -0400
Message-ID: <002301cb5cb2\$8e2eb1b0\$aa8c1510\$@net>
```Very true, it would burn out.

Great explanation, thanks. So this would be a floating ground?

My thinking was the grounds would be common and taking different paths to
the same earth ground (i.e. through the power adapter or supplies).

-----Original Message-----
From: owner-cbm-hackers@musoftware.de
[mailto:owner-cbm-hackers@musoftware.de] On Behalf Of MikeS
Sent: Friday, September 24, 2010 9:15 PM
To: cbm-hackers@musoftware.de
Subject: Re: Technical problem (OT)

If you connected the LED to 12V without any ballast resistors it would
indeed flash; very bright, but only once ;-)

You're still assuming the "grounds" are connected to each other but they are

not; zero volts on the TI side can be anything on the PC side. Each side
only sees various voltages relative to its own ground, and doesn't know or
care which wire (if any) is connected to the other's ground.

Consider this, if GND is 0V on both sides:

Line1: A-TX (-12V) ------ B-RX(-12V)
Line2: A-GND(0V) ------- B-GND(0V)

vs:

Line1: A-GND(0V)----- B-RX(+12V)
Line2: A-TX (-12V) --- B-GND(0V)

No difference, except the polarity is inverted in the second case, just like

reversing the leads on your multimeter where the black wire is equivalent to

"ground".

m
**********************

----- Original Message -----
From: "Scott" <rylos@charter.net>
To: <cbm-hackers@musoftware.de>
Sent: Friday, September 24, 2010 8:39 PM
Subject: RE: Technical problem (OT)

> Hmmmm... Yes, that would make the ground powered like I stated below. But,
> if it were a true ground it would be grounded on the TI85 side, Zero E.
>
> So my answer to the most excellent question would be that the connection
> to
> the LED should be on the 12E side of R3. Is it supposed to flash? Heh...
> But
> even if this is the case there is the polarity issue correct?
>
> -----Original Message-----
> From: owner-cbm-hackers@musoftware.de
> [mailto:owner-cbm-hackers@musoftware.de] On Behalf Of MikeS
> Sent: Friday, September 24, 2010 7:51 PM
> To: cbm-hackers@musoftware.de
> Subject: Re: Technical problem (OT)
>
> You're assuming that the grounds are actually connected together and at
> the
> same potential; without studying it in detail I suspect they're inverting
> the signal. Everything is relative...
>
> Also keep in mind that RS-232 signals are +/- 12V (e.g. pin 3 is normally
> at -12V which will light the LED quite nicely)
>
> m
> ----- Original Message -----
> From: "Scott" <rylos@charter.net>
> To: <cbm-hackers@musoftware.de>
> Sent: Friday, September 24, 2010 5:57 PM
> Subject: RE: Technical problem (OT)
>
>
>> Well, the LED can't work. I was thinking that the pin may be miss-labeled
>> but no... Pin 5 is signal Ground.
>>
>> http://www.diyha.co.uk/electronics/comm1.html
>>
>> Even if the shield had power isn't the polarity wrong?
>>
>> http://www.diyha.co.uk/electronics/comm1.html
>>
>> -----Original Message-----
>> From: owner-cbm-hackers@musoftware.de
>> [mailto:owner-cbm-hackers@musoftware.de] On Behalf Of Ruud@Baltissen.org
>> Sent: Friday, September 24, 2010 4:46 PM
>> To: cbm-hackers@musoftware.de
>> Subject: Technical problem (OT)
>>
>> Hallo allemaal,
>>
>>
>> I think I found the reason for my email problems. A bit further you
>> see "bit......" and that was "bit baCC ngBB MMed". I think there is
>> a porno filter active :)
>>
>>
>> I had to buy a TI-84 for my son for school. Quite interesting, it
>> has a Z80 on board. It has a bit...... USB interface and another
>> bit....... 2-line interface. This particular interface can be
>> connected to the RS-232, please se:
>> http://www.ticalc.org/hardware/cables/serial.html
>> The second site is Dutch but the schematic is more clear IMHO.
>>
>> Why this email? I'm puzzled, I have no idea how this can work well
>> with the LED between the two Grounds.
>>
>> If anybody can explain this, please! Thank you!
>>
>>
>> --
>>    ___
>>   / __|__
>>  / /  |_/     Groetjes, Ruud Baltissen
>>  \ \__|_\
>>   \___|       http://Ruud.C64.org
>>
>>
>>
>>
>>
>>
>>
>>       Message was sent through the cbm-hackers mailing list
>>
>>
>>       Message was sent through the cbm-hackers mailing list
>
>
>       Message was sent through the cbm-hackers mailing list
>
>
>       Message was sent through the cbm-hackers mailing list

Message was sent through the cbm-hackers mailing list

Message was sent through the cbm-hackers mailing list
```